3.1 Freshwater bivalves biodiversity pattern
Each water sample yielded on average 8.1 species (ranging from 0 to 24 species, distribution showed in Figure 1). In only three water samples no bivalve at all could be detected. It was always in still waters, in small pounds. Sites with only one species were either in pounds, or close to the sea (hence possibly brackish), or high upstream the hydrosystem. On the other hand, the richest sites (15 species and over) were always large rivers as shown in Figure 2. Half of the sites had between 5 and 11 species.